Engine systems may be configured with multiple turbochargers coupled to a common manifold to improve engine boost. For example, engines may include twin-turbochargers coupled to parallel intake and/or exhaust passages. Engine control systems may adjust operation of the turbochargers based on a desired boost level.
One example approach for boost control in a variable displacement engine is described by Lamb et al. in US 2007/0074513. Therein, the turbines of two asymmetric turbochargers are connected to an exhaust manifold common to all the engine cylinders. The common exhaust manifold includes a valve for selectively directing exhaust gases to flow through the turbines of one, the other, or both turbochargers based on the number of deactivated cylinders. Specifically, when more cylinders are deactivated, the valve is adjusted to direct exhaust to the turbine of the smaller turbocharger, and when more cylinders are deactivated, the valve is adjusted to direct exhaust to the turbine of the larger turbocharger, or to both turbines.
However, the inventors herein have recognized a potential issue with such an approach. It may be desired to operate the variable displacement engine with twin parallel turbochargers to improve the boost provided to each group of cylinders of the engine. As such, if a twin turbocharger system is used, when some cylinders are deactivated, the valve of Lamb et al. may not be able to direct sufficient exhaust to a compressor to provide the desired amount of boost. Further, the boost pressure from the turbocharger compressor coupled to the enabled cylinder group may cause backflow of air through the turbocharger compressor coupled to the disabled cylinder group. As such, this may degrade overall engine boost.
Thus, in one example, the above issue may be at least partly addressed by a method of operating a boosted engine including first and second parallel intake passages leading to first and second cylinder groups respectively. The first intake passage may include a first throttle downstream of a first turbocharger compressor, while the second intake passage may include a second throttle downstream of a second turbocharger compressor. In one embodiment, the method comprises, deactivating the first cylinder group, and adjusting each of the first and second throttle responsive to the deactivation.
For example, the first throttle leading to the disabled first group of cylinders may be fully closed while the throttle leading to the second group of cylinders may be at least partially opened, the opening based on the number of deactivated cylinders on the first cylinder group, and a desired amount of boost. Further torque adjustments may be made with a third air intake throttle. In alternate embodiments, the first and second throttles may be positioned upstream of the respective turbocharger compressors. In still other embodiments, a backflow valve may be adjusted in lieu of a backflow throttle.
In this way, by adjusting the backflow valves and/or throttles, a manifold pressure at the disabled cylinder group may be raised while reducing pumping losses. By reducing backflow of air through the boosted VDE engine systems during cylinder deactivation conditions, engine boosting efficiency may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.